With increasing demands for bandwidth in communications and computing, there is an increasing need for fast signal processing systems. Two common signal processing functions are the conversion of serial data to parallel data, and the conversion of digital data to an analog signal. S/P conversion is important at the interface of computation and communication systems. Computers typically operate on parallel data, while long distance transmission is typically done through serial connections. D/A conversion is useful in the generation of arbitrary waveforms, and also in certain architectures of analog-to-digital (A/D) converters. As electrical components reach their performance limits it is becoming necessary to perform signal processing through optical methods.
Certain embodiments allow the optical transmission of serial data at rates up to 40 Gb/s across a single carrier channel. Current electrical S/P converters are only able to operate at bit rates around 2.5 Gb/s. In certain embodiments an optical method for S/P conversion has been demonstrated at rates of 1 Tb/s using a surface-reflection optical switch. This method has issues with low bit contrast ratios and crosstalk between the parallel outputs. As a result, there is still a need for new devices which can match high transmission rates, while maintaining high bit contrast, and low crosstalk.
While there has been much work in A/D conversion, D/A conversion has received less attention. Alternative embodiment has demonstrated the use of optical correlation to recognize bit patterns. This method, however, requires a separate module for each bit pattern, resulting in 2N−1 modules, where N is the number of bits in each digital word. Another embodiment demonstrated uses a probe pulse through a series of nonlinear optical loop mirrors which are controlled by the bit pattern. Once again the number of components in the device grows by 2N−1, making high resolution D/A unreasonable. There is therefore a need for high speed D/A converters which grow linearly with respect to number of bits as provided by this invention.